'\" et
.TH POSIX_MADVISE "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
posix_madvise
\(em memory advisory information and alignment control
(\fBADVANCED REALTIME\fP)
.SH SYNOPSIS
.LP
.nf
#include <sys/mman.h>
.P
int posix_madvise(void *\fIaddr\fP, size_t \fIlen\fP, int \fIadvice\fP);
.fi
.SH DESCRIPTION
The
\fIposix_madvise\fR()
function shall advise the implementation on the expected behavior of
the application with respect to the data in the memory starting at
address
.IR addr ,
and continuing for
.IR len
bytes. The implementation may use this information to optimize handling
of the specified data. The
\fIposix_madvise\fR()
function shall have no effect on the semantics of access to memory in
the specified range, although it may affect the performance of access.
.P
The implementation may require that
.IR addr
be a multiple of the page size, which is the value returned by
\fIsysconf\fR()
when the name value _SC_PAGESIZE is used.
.P
The advice to be applied to the memory range is specified by the
.IR advice
parameter and may be one of the following values:
.IP POSIX_MADV_NORMAL 6
.br
Specifies that the application has no advice to give on its behavior
with respect to the specified range. It is the default characteristic
if no advice is given for a range of memory.
.IP POSIX_MADV_SEQUENTIAL 6
.br
Specifies that the application expects to access the specified range
sequentially from lower addresses to higher addresses.
.IP POSIX_MADV_RANDOM 6
.br
Specifies that the application expects to access the specified range in
a random order.
.IP POSIX_MADV_WILLNEED 6
.br
Specifies that the application expects to access the specified range in
the near future.
.IP POSIX_MADV_DONTNEED 6
.br
Specifies that the application expects that it will not access the
specified range in the near future.
.P
These values are defined in the
.IR <sys/mman.h> 
header.
.SH "RETURN VALUE"
Upon successful completion,
\fIposix_madvise\fR()
shall return zero; otherwise, an error number shall be returned to
indicate the error.
.SH ERRORS
The
\fIposix_madvise\fR()
function shall fail if:
.TP
.BR EINVAL
The value of
.IR advice
is invalid.
.TP
.BR ENOMEM
Addresses in the range starting at
.IR addr
and continuing for
.IR len
bytes are partly or completely outside the range allowed for the
address space of the calling process.
.br
.P
The
\fIposix_madvise\fR()
function may fail if:
.TP
.BR EINVAL
The value of
.IR addr
is not a multiple of the value returned by
\fIsysconf\fR()
when the name value _SC_PAGESIZE is used.
.TP
.BR EINVAL
The value of
.IR len
is zero.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
The
\fIposix_madvise\fR()
function is part of the Advisory Information option and need not be
provided on all implementations.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fImmap\fR\^(\|)",
.IR "\fIposix_fadvise\fR\^(\|)",
.IR "\fIsysconf\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<sys_mman.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
